Sir Paul McCartney has flown to New York to be at the bedside of the man known as "the Fifth Beatle" who was last night fighting for his life in hospital.

For more than 40 years, Neil Aspinall controlled the vast empire of the Fab Four.

A quiet, bespectacled accountant, he was their chief confidant and business adviser, took part in some of their more rebellious pranks and even sang backing vocals on Yellow Submarine.

But Mr Aspinall, 65, is believed to be suffering from lung cancer and has flown to New York from his London home for treatment at Manhattan's prestigious Memorial Sloan-Kettering Cancer Centre.

A family friend said that Sir Paul had been to visit. "I understand that Paul saw him in hospital in New York," the friend said. "Paul will be devastated if he doesn't beat this. They have been mates ever since they were schoolboys in Liverpool."

The news of Mr Aspinall's condition will have come as a shattering blow for Sir Paul who has seen several loved ones and friends lose battles with cancer.

In 1998, breast cancer claimed his first wife Linda at 56, then George Harrison died of lung cancer at the age of 58 in 2001.

Cancer also claimed the life of the Beatles' long-time Press agent Derek Taylor in 1997 and Ringo Starr's first wife, Maureen Starkey, died from leukemia in 1994 when she was 47.

The family friend said Mr Aspinall used to smoke, but gave up years ago.

Mr Aspinall was expected to build a career as a conventional accountant when he struck up a friendship with the young McCartney and Harrison after they all gained places at the Liverpool Institute.

Mr Aspinall once joked that they initially bonded over the illicit cigarettes that they would smoke behind the school's air-raid shelters.

"By the time we were ready to take the GCE exams, we'd added John Lennon to our 'Mad Lad' gang," he said.

Once they became the Beatles, they also experimented with drugs. Aspinall observed: "Quite a bit of marijuana was being smoked. It made recording a bit slower, but it didn't affect the quality of the work."

John Lennon claimed they smoked marijuana in the lavatories at Buckingham Palace when they collected their MBEs in 1965.

Mr Aspinall started work for the band as the £1 ($2)-an-hour driver of their battered blue Commer van.

He had an affair with Mona Best, mother of the band's first drummer Pete Best, and in 1962 they had a son.

He was with The Beatles ­ now with Ringo Starr as drummer ­ as they conquered America and even stood in for Harrison when the guitarist fell sick during the rehearsals for their first major TV show.

He also contributed to some recordings, playing percussion on Magical Mystery Tour and belting out the Yellow Submarine chorus.

But his real genius was as a money man and in 1968 he took over Apple Corps, the company the Beatles had set up to manage their business interests.

He took computer giant Apple Inc to court three times over image infringement and, in winning two of the suits, the Beatles' company was awarded more than £13. 5million ($27 million).

Just 11 months ago, he finally quit his job as Apple chief executive to run a small film company, Standby Films, from his home in Twickenham, Middlesex.